This application is based on Japanese Patent Application No. 2009-015930 filed with the Japan Patent Office on Jan. 27, 2009, the entire content of which is hereby incorporated by reference.
1. Technical Field
The present invention relates to a system for displaying information for quality control of a substrate produced in a production site of component-mounted substrates, and also relates to a method for displaying the information.
2. Related Art
Recent portable telephones and digital household appliances are smaller in size and have more and more functions. Accordingly, production of small substrates mounted with micro components with high-density is required in production sites of component-mounted substrates.
In such substrates, even a slight change in the supply of materials or the condition of jigs may deteriorate the quality of the substrates. Therefore, it is necessary to swiftly detect decrease in the precision of each process and find out a cause of the decrease.
In view of the above problem, Japanese Unexamined Patent Publication No. 2006-343152 describes a technique including the steps of measuring the amounts of solders printed at a plurality of positions of a plurality of substrates and displaying a histogram representing a frequency distribution of the measured values. Further, Japanese Unexamined Patent Publication No. 2006-71416 describes a technique including the steps of measuring the height, size, and volume of solders printed on a substrate and displaying a layout chart representing deviations between the measured values and reference values in such a manner that the levels are shown by a plurality of shades of gray.
Further, there is a method called stratified analysis, i.e., a quality control method widely employed at ordinary production sites. This method includes the steps of classifying constituent elements on a substrate (such as individual pieces, components, and electrodes) and productions conditions (such as lots, jigs, and time periods of production) into a plurality of conditions, making a graph of averages of measured values and unevenness for each condition, and comparing the graph in each condition. Then, when a difference of distribution is found between the graphs under a certain classified condition, an operation is carried out to find out specific cause, because the elements used in the classified condition are considered to have something to do with the decrease in the quality.
The decrease in the quality of a component-mounted substrate may be concentrated on a particular portion or a particular component, or may be not. In some cases, a time period in which the quality deteriorated can be identified, for example, such time period may be determined to be after the lot changes over or after a jig is replaced. But in other cases, the time period of the deterioration in the quality cannot be identified. In order to identify the cause of the deterioration in the quality in various circumstances as described above, it is necessary to understand both of variation of measured values within each substrate (hereinafter referred to as “variation within substrate”) and variation of measured values between substrates (hereinafter referred to as “variation between substrates”).
In the method described in Japanese Unexamined Patent Publication No. 2006-343152, measured values at a plurality of positions on a plurality of substrates are grouped and displayed as one histogram, and therefore, it is considered that neither the variation within substrate nor the variation between substrates can be recognized. In the method described in Japanese Unexamined Patent Publication No. 2006-71416, the variation within substrate can be recognized, but it is difficult to recognize the variation between substrates.
In a generally-used stratified analysis, the variation within substrate and the variation between substrates can be obtained by classifying a plurality of conditions. However, in order to narrow the reason of deterioration in the quality, it is necessary to arrange many classified conditions, and it may take a lot of time to identify the reason. Further, the stratified analysis is not suitable for checking whether there is any deterioration in the quality of products produced in a production line currently operating. Even if the stratified analysis is used for such purpose, it is difficult to efficiently perform check operation.